Attempted to change debit order date for a year

Absolutely shocking service. I've been trying to change my debit order for a year yet every month they attempt to debit the 25th when I have no funds putting my account in minus because my account goes into minus so often it effects my credit score and they have now frozen my revolving loan saying I don't qualify for credit because my account is in bad standing because of them!. I spoke to one of their representatives and they simply said they "checking if I have funds available". This is nonsense and a lie. I have finally managed to change the debit date but my account remains in bad standing due to failed debits and the representative just says it is what it is and I will have to pay the fees despite me attempting to change this for a year. Will be changing banks.